We tried using our new 2007 4-stroke Eton Viper 90R this weekend, and it developed a problem not wanting to accept throttle (on cars we used to call this a "flat spot"). It starts up and idels fine, but just bogs out when you advance the throttle. If you repeatedly give it short small bursts of throttle, you can sometime coax it up to the hiher RPM, but then it stalls as soon as you throttle back. Last weekend it seemed to happen after it was running for a while, but this weekend the problem was very severe, but finally went away after about 30-45 minutes.

The temperature was cold outside (about zero Fahrenheit), and the bike has a manual choke (which helped a bit to keep it running at idle, but had no effect on the bogging problem.

Does anyone have any ideas about this?

Thanks,

 

Try adj. the air/fuel mixture screw i had a 70cc viper doing the same it's 2 stroke though i turned in the air/fuel screw it idled up then i turned the idle screw down alittle t'll it was right on. Worth a try..

 

OK, thanks a bunch superbombman, I'll give it a try and report back.

 

An update: I took it in to the dealer, who cleaned the carb (and found some dirt in the low RPM jet), but also said (to my surprise) that when the gas tank is low and you accelerate (or decelerate) the little bit of gas at the bottom of the tank sloshes to the front or back, and thus the motor becomes starved for gas. We'll see - I will fill it right up (with hi-test 91 Octane gas) and see if the problem is gone.

 

Well, we tried it again last weekend (after the dealer had adjusted it), and the problem remains. The quad starts fine and then shifts into gear finer and runs Ok for a little while until it warms up, but then starts to sputter and die if I don't pump the throttle or keep it at least partly open. And, since a sfety mechanism shuts off the motor if you shift into gear with the revs too high, I can't get it into gear - I have to rev it to keep the motor running, but then it shuts off as soon as I move the lectric gear switch over to forward or reverse.

I left a message at the Eton dealer, and the mechanic left a return message saying to change the sparkplug.

So now the story has gone from "it was too low on gas and the gas pickup was getting exposed" to "it's the sparkplug."

I'll try changing the plug and see what happens, and also playing with the idle and mixture screws. (Things may be different as well because the quad is now at home where the temp is above freezing, whereas on the weekend we were up at the cottage in temps of about 0 degrees F or so.)

 

Do the 2007s still have the electric choke as I have heard of people having problems with it sticking.

 

The dealer said it did not have an electric choke, but it sure doesn't look mechanical to me!

(Superbombman, the dealer also said that he had assured that the carb idle and mixture screws were to spec.)

Also, I bought the new spark (NGK) plug that the dealer recommended, but then decided to try the bike again before installing the new plug, and the problem was now gone! I rode the bike around here in Toronto for over a half an hour (more than long enough for it to fully warm up), and no problem! Even with a fast WOT from idle, the bike accelerated nicely with no bogging at all.

So, now my theory is that either there was a gel pack that has finally disolved properly, or the cold weather up at the cottage was the problem. (-20 degrees C at the cottage versus about 2 above here in Toronto.) If the latter is the case, then maybe I have to adjust the carb ring each winter and then back again each Spring? (Something I would not be happy about.)

 

I spoke to a friend this weekend who was a snowmobile dealer for many years and is good at small engine repair, and he suggested that bogging out may be due to little bits of iron/steel filings getting stuck in the carb on new machines. Has anyone heard of this?

BTW, we drove the Viper up at the cottage this weekend (where it was "warm" - just at or just below freezing), and it ran fine except that after about a half-hour it idled a bit rough, so I may try cranking up the idle adjustment screw a bit.

 

Hey, I just joined this forum because I recently purchased the same atv for my son and it has been exhibiting the same problem. I live in WPB FL. by the way, so I can tell you that cold weather is not a factor... I've had it back to the dealer twice now and both times they claim that they have not been able to find a problem with it, not only that but it supposedly starts and runs perfectly while in the shop. However, once back at home it still has the same issues, and like yours, it's an on and off thing, but we are afraid to get too far from home since we have had the pleasure of pushing it back twice now... anyway, if you do finally locate the cause, please post the solution...Thanks!
Roxy

 

Check,

To me it sounds like being whee you were in elevation and it being cold it was running lean. Now its warmer and you are at a lower elevation it is rich. I have seen this alot. I think if you want to run in a higher elevation and in cold weather you need to rejet for those conditions. Most quads are jetted for certain temps and elevation. If you go below the jetting specs it wil run lean and bog no matter what you do. I dont think there is anythingwrong with the quad. It just needs to be jetted for your conditions.